Magnetic recording-reproducing transducer



Oct. 3, 1950 E. E. MAsTERsoN A 2,524,063

MAGNETIC RECORDING-REPRODUCING` TRANSDUCER Filed Nov. 50, 1948 i) li MUMwlmi lNVENTOR EARL E MASTEHSDN ATTORNEY Patented Oct. 3, 1950 MAGNETICREORDING-RPRODUCING TRANSDUCER Earl E. Masterson, Palmyra, N. J.,assigner to Radio Corporation of America, a corporation of DelawareApplication November 30, 1948, Serial No. 62,754

8 Claims. (Cl. 179-1002) This invention relates to magneticsound-recording and reproducing systems and has special reference to theprovision of improvements in systems designed to handle plural-tracktape records.

The transducer or magnetic applicators employed in` present day magneticphonographs for recording, reproducing and erasing purposes usuallycomprise two stacks of C-shape lamina tions assembled in the form of aring; the thick ness of the stacks and hence of the ring being adjustedto correspond to the width of the sound track which the applicator isdesigned to serve. Although ring-type applicators of the type de,-scribed contain two air-gaps, only one of the gaps can be used and it istherefore necessary, when using this type of applicator in conjunctionwith dual-track records, to employ either (a.) two erasing applicatorsand a movable recording reproducing applicator or (b) tworecording-reproducing applicators and a movable erasing applicator. Inany case all dual-track magnetic phonographs designed for both recordingand re-k producing have heretofore necessarily employed three or moremagnetic applicato-rs.

The principal object of the present invention is to provide a magneticphonograph wherein but two (instead of three) magnetic-applicators arerequired for recording, reproducing and erasing a dual-track record.

'A related object of the inventio-n isto provide a double-ended magneticapplicator wherein l the polar portions are constructed and arranged toservice separate ones of the soundtracks of a dual track record.

The foregoing objects are achieved in accordance with the invention bythe provision of a magnetic applicator comprising a bi-part laminatedmagnetic structure having a pair of confronting pole portions at one endand another pair of confronting polar portions at its other end; thepolar portions at one end being offset from the polar portions at theother end a dis` tance corresponding substantially to one half the widthdimension of the record and by so mount ing the applicator that each ofits two pairs of polar portions is always in line with the particularsound-track that it is des-igned to serve.

Certain preferred details of construction together with other objectsand advantages will be apparent and the invention itself will be bestunderstood by reference to the following speciiication and to theaccompanying drawing, wherein:

Fig. 1 is a view in perspective of a double-ende ed` magnetic applicatorconstructed iii-accordance with the principle of the invention forservicing a dual track tape-like record.

Fig. 2 is a section taken on the line 2-2 of Figs.

Fig. 3 is a section taken on the line 3 3 of Fig. 2.

Fig. l is a view in perspective ofthe bi-part magnetic core member ofthe applicator andy Fig. 5 is an elevational view of a reeling systemfor a dual-track magnetic tape record show.-v ing one manner in whichthe magnetic-applicator of the invention may be` presented to separatesound tracks on a `flexible tape-like record. The specific form of thereeling system herein shown is claimed in the copending application ofEarl E. Masterson and Noel Urquhart, Serial No. 84,634, led March 3l,1949.

The drawing shows a, bi-part laminated magnetic-core structurecompris-ing two C-shape pieces l and 2, arranged in juxtaposition,thelaminations in each piece being cut and stacked at an angle (as moreclearly shown in Fig. 2),

so that the confronting polar faces 3 and 4 at` one end of the structureare offset (in a vertical direction as viewed in Figure 2) from the,confronting polar faces 5 and E at the other end a distancecorresponding approximately to the common thickness dimension or" thetwo pieces. After the laminations are stacked at an angle, the outerextremities of thecore structure adjacent to the polar faces are dressedto provide smooth, tape contacting surfaces. Stated more specifically,the discrete polar faces 3 and 4 or 5 and 6, which define oppositelylocated nonmagnetic gaps 8 and 9, respectively, in the struc,- ture, aredisposed on opposite sidesv of, and parallel to, a first reference planeP--P (Figure 3), and the respective tape contacting surfaces aredisposed, in accordance with the present invention, on opposite sides ofa second reference plane PP (Figure 2) drawn through the corestructureI-2 normal to the first reference plane and` to a third reference planeP-P (Figures 2 and 3) which is normal to the firstA reference' plane P-Pand tangent to either of the tape contacting surfaces at the gaptherein.

In order to reduce the possibility of cross-talk between the soundtracks the thickness dimension of the magnetic core should preferably bevery slightly less than one-half the widthy of the 3 thickness of thecore was approximately .025 less than one-half the width of the tape.This permitted the use of a clearance (unmagnetized) space of .030 alongthe center of the tape between the two sound tracks and a clearancespace of .010 between the outer edge of each track and the adjacent edgeof the tape.

As shown more clearly in Figs. 4 and 1, the outer or tape contactingsurfaces of the core structure I 2 adjacent to its separate pairs ofpolar faces 3 4, 5 6 are preferably made at least slightly convex sothat the tape record l (Figs. 2 and 5) may be subject to tension inpassing over the non-magnetic gaps 8 and 9 between the said pairs 4ofpolar faces. As in standard practice the eld coils I and II for themagnetic core may be wound on separate coil forms I2, I3 (Figs. l and 3)on the mid-sections of the C-shape parts I and 2 of the core.

The bi-part magnetic core of the applicator, and its field coils I0 andII, are preferably mounted in a casing or housing I5 which is providedon each of its opposite ends with a, pair of outstanding flanges IIS-Il,|8 I9 for guiding the record tape 'I past the separate air gaps 8 and 9.In the instant case the housing for the core and its coils comprises apair of mica side walls 20, 2l and upper and lower body parts 22 and 23(Fig. l) constituted of aluminum cr other light weight non-magneticThese parts 22 and 23 have diametrically opposed convex end-wallportions 24 and 25 which lie flush with the convex tape contactingsurfaces of the ends of the magnetic core adjacent to the polar faces 34, 5 6. Each of the convex wall I portions 24, 25 occupies that half ofthe space between the guide members IG-I'I, I8 I9 which is allotted tothe sound track that is served by the opposite pair of pole faces. Theopposed lateral surfaces of the dependent end walls 24 25 of the housingI5, have the same angle of tilt as the magnetic core I 2 and the core isclamped therebetween by non-magnetic screws 26 and 2l which extendthrough the hollow inner portion of the core. cure an insulatingterminal board 28 to a central rib 29 on the outer surface of the lowerpart 23 of the housing. The terminal board or socket 28 is preferably ofthe same shape and dimensions as the bottom of the casing and thepresence of a space 30 between the socket 28 and the said bottom surfaceobvates the possibility of a short circuit between the casing and theinner terminals of the lugs 3| and 32 to which external connections aremade to the leads 33 34 g of the coils I0 and II. A screw hole or otheraperture 35 is provided at the center of the casing I5 for attaching theunit to a mounting plate 36 (Fig. 5).

Fig. 5 shows how two magnetic applicators I5 I5, constructed inaccordance with the invention, may serve as the erasing, recording andreproducing heads for both sound tracks of a plural-track record '1.Here the applicators which are immovably mounted in line with each otheron the back plate 36, project through separate arcuate apertures 31 and38 in a pivotally mounted front plate 39. There is a capstan or drivingpulley 4D for the tape mounted adjacent to the pivot of the plate 39 andtwo pairs of guide rollers II-42, 43 44 mounted in spaced apart relationon different radii of the said plate adjacent to the opposite ends ofthe slots 3l and 38 through which the magnetic applicators I5 and I5project. The rollers 4I 42 (or 43 44) and material.

These screws 26 2'I also serve to se- I the capstan 40 define a, path inthe form of an open loop around which the record I travels with itsmagnetizable surface presented to the interior of the loop. Thus, whenthe pivoted front plate 39 is swung to the right, as it is shown in Fig.5, the guide rollers 4I and 42 urge the tape into contact with the leftend of each of the applicators I5 and I5', and the tape I is drawn bythe capstan 40 over the gap between the polar faces at that end of theapplicators. Conversely, when the plate 39 is swung to the left the tapeis moved out of contact with the left ends of the applicators and isurged by the other pair of rollers 43 and 44 into contact with theconvex ends on the right side of the applicators. Since, as previouslyset forth, the opposite ends of the applicators are offset from eachother, they serve different longitudinal halves of the magnetizablesurface of the tape. In the instant case, the left end of the rstapplicator I5 serves as the erasing head for one of the sound trackswhen the tape is driven in the forward direction and its other endserves as the erasing head for the other track when the tape is drivenin the opposite direction. Similarly, the left end of the secondapplicator I5 serves as a combined recording and reproducing head forthe first mentioned track when the tape is running forward and its otherend serves as the recording and reproducing head for the other trackwhen the tape is running in the reverse direction.

From the foregoing it will be apparent that two of the double endedmagnetic applicators of the present invention will do the work of threeprior art applicators. Furthermore, it will be apparent that the presentinvention (a) simplifies hum-balancing problems, since one applicator isused for both tracks (b) simplifies the associated amplifiers since noswitch is required to change the circuit from one track to the other (c)because the same coils are used for both tracks, the sensitivity orresponse of the two tracks is the same and (d) the life of theapplicators is doubled because of its dual wearingsurfaces.

What is claimed is:

1. A magnetic applicator for a flexible magnetic record comprising acasing having a pair of oppositely located, outwardly convex end wallsconstituted of non-magnetic material upon which the record may traveland having diametrically opposite openings disposed on opposite sides ofa median plane drawn through said convex end walls, and a laminatedmagnetic structure mounted within said casing and having a pair ofconfronting convex pole portions presented to said diametricallyopposite openings and forming a continuation of the convex end walls ofsaid casing.

2. The invention as set forth in claim 1 and wherein each of saidnon-magnetic end walls of said casing are provided with a pair of spacedapart guide members between which said flexible record travels in itsjourney over said diametrically opposite pairs of magnetic pole pieces.

3. A transducer comprising a magnetic structure having oppositelylocated polar end portions, each of said end portions having anon-magnetic gap therein, the boundaries of each of said gaps beingdefined by a pair of confronting pole faces, the outer extremities ofsaid end portions adjacent to said gaps constituting oppositely disposedtape contacting surfaces, the confronting faces of each pair beingdisposed on opposite sides of a common reference plane through both ofsaid gaps, substantially al1 of one of said tape contacting surfacesbeing disposed on one side of a second reference plane normal to saidfirstmentioned plane and the other of said tape contacting surfacesbeing disposed on the opposite side of said second reference plane, saidrst and second reference planes being mutually normal to a thirdreference plane which is ltangent to either of said tape contactingsurfaces at the gap therein.

4. A transducer for servicing the separate magnetic sound-tracks of adual-track record of the type Whereon said magnetic tracks are disposedin spaced apart relationship on opposite sides of the centrallongitudinal axis of a tape-like base, said transducer comprising amagnetic structure having a pair of oppositely located end portions,said structure having a rst non-magnetic gap in one of said endportions, the boundaries of said first gap being defined by a first pairof confronting pole faces which terminate said inagnetic structure atthe end adjacent to said first gap, said structure having a secondnon-magnetic gap in the other of said end portions, the boundaries ofsaid second gap being defined by a second pair of confronting pole faceswhich terminate the magnetic structure at the end ad jacent to saidsecond gap, the outer extremities of said end portions adjacent to saidgaps constituting oppositely disposed tape contacting surfaces, all ofsaid pole faces lying substantially parallel to a reference plane whichlies through both of said gaps, substantially all of one of said tapecontacting surfaces being disposed on one side of a second referenceplane normal to said first mentioned plane and the other of said tapecontacting surfaces being disposed on the opposite side of said secondreference plane, said first and second reference planes being mutuallynormal to a third reference plane which is tangent to either of saidtape contacting surfaces at the gap therein.

5. The invention as set forth in claim 4 and wherein the thicknessdimension of said magnetic structure as measured along the tapecontacting surfaces is less than one-half the Width dimension of saidtape-like base of said dualtrack record.

6. The invention as set forth in claim 5 and wherein said thicknessdimension corresponds substantially to the width dimension of one of themagnetic sound-tracks on the dual-track record which said transducer isdesigned to serve.

7. The invention as set forth in claim 4 and wherein a pair ofparallelly arranged flanges are mounted adjacent to each of said ends ofsaid magnetic structure for guiding said tape-like record past saidnon-magnetic gaps along a path normal to said outer edges of said polarfaces.

8. The invention as set forth in claim 4 and wherein said secondreference piane extends along said central longitudinal axis of saidrecord when said record is in its said path between said parallellyarranged flanges.

EARL E. MASTERSON.

REFERENCES CITED The following references are of record in the le ofthis patent:

FOREIGN PATENTS Number Country Date 622,623 Germany Dec. 2, 1935 725,830Germany Sept. 30, 1942

